1. Field of the Invention
The present invention relates generally to the field of holders for roll type print media, roll type print media cassettes, and related printing devices, and more particularly to a system for printing on a thermal print film wound in a roll shape.
2. Description of the Background Art
Conventional print media, such as printing paper and thermal print film, are often wound in the shape of a roll (hereinafter, referred to as roll-type print media). Various printing apparatuses corresponding to the roll type print media have been also manufactured. The printing apparatus has the advantage of being miniaturized entirely, since the space to load a print media (hereinafter, referred to as loading space) is small in comparison to other printing apparatuses using paper stock or print film cut into a predetermined size (e.g., A4 size). The roll-type printing apparatus also has the advantage of loading a large quantity of print media in a small loading space.
Among available roll-type print media, print film wound in the shape of a roll can be problematic in that it may easily become unwound due to the very low coefficient of friction and adhesion between adjacent surfaces on the roll. For this reason, roll-type print media can be difficult to load in a printing apparatus in such a manner that the print film does not become unwound. This problem is especially acute where roll-type print media is replaced frequently, and work efficiency for replacement is concomitantly decreased. This problem can also be especially severe where transparent print media (as for printing x-ray images) is installed, since conventional printing apparatuses requiring roll-type print media normally detect the existence of an installed roll using a light sensor, and transparent film partially unwound can go undetected when a light beam emitted from the optical sensor penetrates the transparent print layers film without detection.
One available approach to solving the above-described problem comprises a method of detecting the existence of roll type print media using a contact sensor within the printing apparatus. However, the roll-type print media is unstable in that it rolls within the loading space and changes in diameter throughout the period of its consumption. Thus, even if a contact sensor is used to detect the existence of the roll-type print media in the conventional printing apparatus, it is difficult to place the contact sensor into reliable contact with the roll type print media. As a result, efficiently and reliably detecting the existence of roll-type print media remains a challenge.